It has been previously described that lower alkanes can be directly converted into higher hydrocarbons using a molybdenum-modified medium pore-size zeolite catalyst.
Wang (1993) Catal Lett 21, 35-41, for instance, describes the catalytic conversion of methane into benzene under non-oxidizing conditions using a ZSM-5 zeolite catalyst on which molybdenum has been deposited.
A major drawback of the use of molybdenum-modified medium pore-size zeolite catalyst for the aromatization of lower alkanes is that coke is deposited on the catalyst surface which quickly reduces catalyst activity.
Shu (2002) Chemistry Letters, 418-419 describes that de-alumination by acid reflux of Mo-loaded zeolites like ZSM-5 and MCM-22 leads to decreased coke formation in methane aromatization reactions. Shu teaches that this reduction in coke formation is caused by a reduction of the number of Brønsted acid sites on the catalyst surface.
WO 02/10099 describes that the catalyst activity in a methane aromatization process can be stabilized by activating the molybdenum-loaded ZSM-5 catalyst with a combined stream which comprises over 25 mole-% of hydrogen and methane prior to contacting the catalyst with the methane feed.